The present invention relates to a hard contact lens material, and more particularly to a hard contact lens material having a high oxygen permeability.
A glass material hitherto has been mainly used as a hard contact lens material, but nowadays polymethyl methacrylate which is superior in cutting-processability and flexibility to the glass material and is light is used as a hard contact lens material.
However, since the hard contact lens material comprising polymethyl methacrylate is poor in oxygen permeability, the obtained contact lens has a problem that a metabolism disorder of the cornea tissue occurs when the contact lens is used on the surface of a cornea tissue for a long period of time.
Thereupon the study and the development of a hard contact lens material having a high oxygen permeability which can be substituted for the contact lens material comprising polymethyl methacrylate has been attempted, and in these days, for example, a contact lens material comprising a copolymer mainly made of fluorinated (meth)acrylic acid esters, a contact lens material which is produced by first introducing a vinyl polymerizable group into (poly)organosiloxane and then copolymerizing the (poly)organosiloxane with other vinyl monomers, and the like are obtained.
Though the oxygen permeability of the copolymer comprising (poly)organosiloxane in which vinyl polymerizable groups are introduced and other vinyl monomers is not so high, the copolymer enables improved oxygen permeability of an obtained hard and optically clear acryl resin, to promote the oxygen permeability to a cornea when it is used as a hard contact lens which is contacted with a cornea and to prevent the lowering of a cornea function caused by the lack of oxygen.
However, a large amount of acryl monomer is needed in order to copolymerize (poly)organosiloxane in which vinyl polymerizable groups are introduced, with the acryl monomer and to give a sufficient oxygen permeability as a contact lens. As a result, the obtained copolymer has some problems such as inferiority of processability at the time of producing a contact lens and lowering of intensity as a lens. On the other hand, for the sake of maintaining the hardness which can be tolerable for the processability when producing a lens, it is impossible to be added a large amount of the (poly)organosiloxane in which vinyl polymerizable groups are introduced, in the acryl monomer, and further, a hard contact lens material having an oxygen permeability sufficient for extensively wearing has not yet been obtained.
On the other hand, a hard contact lens material in which fluorinated (meth)acrylic acid esters are used shows excellent hardness properties. However, it cannot be used in a contact lens which is extensively worn on the surface of a cornea tissue since the oxygen permeability is low. Further, though it is disclosed in U.S. Pat. No. 4,433,125 (Ichinobe et al) that a copolymer of the fluorinated (meth)acrylic acid esters and the (poly)organosiloxane in which vinyl polymerizable groups are introduced shows a very high oxygen permeability and is relatively excellent in hardness, the oxygen permeability is not sufficient for the extensive wearing.
The present invention is accomplished in order to remove the above-mentioned disadvantages and to obtain a hard contact lens which comprises materials having a preferable hardness and hard quality as a hard contact lens and higher oxygen permeability than prior oxygen permeable hard contact lenses.
As the results of my researches, I have eventually found that when a copolymer which comprises at least two kinds of fumaric acid diesters at least one of which is a dialkyl fumarate as main components are employed as a contact lens material, the obtained contact lens material shows excellent oxygen permeability and has preferable mechanical strength as a contact lens.
These and other objects of the present invention will become apparent from the description hereinafter.